<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>过渡案例-进度条</title>
    <style>
        .bar {
            width: 150px;
            height: 15px;
            border: 1px solid red;
            border-radius: 7.5px;
            padding: 1px;
        }
        .bar-in {
            width: 50%;
            height: 100%;
            background-color: red;
            transition: width 0.25s linear;
        }
        .bar:hover .bar-in{
            width: 100%;
        }
    </style>
</head>
<body>
    <div class="bar">
        <div class="bar-in">

        </div>
    </div>
</body>
</html>